1. Field of the Invention
The present invention relates to a semiconductor wafer basket station used for moving and transfering wafers in the process of manufacturing semiconductors.
2. Background Information
A wafer basket has been widely used to transport semiconductor wafers, to supply them for inspection or treating, and to receive them after inspection or treatment has been completed. The wafer basket is also called as a wafer carrier.
It is well-known that different wafer baskets are made for different diameter semiconducter wafers, each wafer basket receiving a number of semiconductor wafers, in most cases 25 wafers, and supporting each of them, with a narrow space between adjacent wafers.
FIG. 1 shows a perspective view of such a conventional wafer basket standing with semiconductor wafers therein.
When one or more of wafers must be taken out from the wafer basket station, it is advantageous to know beforehand whether a wafer or wafers is (are) contained in each of the wafer columns of the wafer basket. If so, failure of a wafer inserting and removing robot to remove a wafer from an empty location may be avoided. And collision of wafers may also be avoided.
In order to confirm the existence of wafers when using an elevating means to elevate a wafer basket, there has been a need for a detecting device for detecting the existence of wafers in the wafer basket. The inventors of the present invention have studied this need.
FIG. 2 is a schematic view showing the basic structure and the principle of the operation of a conventional wafer detecting device in a wafer basket. In the device shown, a reflection type sensor 25 or 26 is disposed so that its optical axis faces towards a center of a semiconductor wafer 15.
With this structure, by the movement of a wafer basket a semiconductor wafer 15 is brought to an optical axis of the sensor 25 or 26, and the sensor receives a reflection light from the wafer 15. Thus the existence of the wafer 15 may be confirmed.
However, the thickness of a wafer is as small as on the order of 0.5 mm, or so, and moreover wafers of various diameters are frequently used. Further, an orientation flat is formed on part of the circumference of a wafer to determine the orientation of the pattern formed on the wafer. These issues raise difficulties in the above mentioned device shown in FIG. 2.
If the diameters of the wafers differ, reflected; light may be still obtained as long as the optical axis of the reflection sensor 25 or 26 is pointed towards the center of the semiconductor wafer. However, because of the difference in the distance to the wafer, the quantity of reflected light varies with the diameter.
If the center of a wafer displaced into a position as shown by the broken line in FIG. 2, it becomes difficult to obtain any reflected light.
In order to avoid the influence of the orientation flat on the circumference of the wafer, two reflection type sensors 25 and 26 may be used so as to receive reflected light by either of the sensors 25 and 26. However, when the position of the wafer is displaced as in FIG. 2, similar problems arise.
In order to take out semiconductor wafers one by one, the height of an elevating device supporting the wafer basket must be adjusted so that the height of the wafer to be taken out is suitable for the operational position of a take-out robot.
It is troublesome to adjust the height each time when taking out a wafer, so it is wise to precisely determine the initial height of the elevating device at the start of operation of the device. The elevating device may then be moved for pitches corresponding to a received semiconductor wafer by a pulsed motor.
A wafer basket having an elevating device which supports and elevates the wafer basket provided with a fine adjustment for the initial stop position of the elevating device is known.
FIG. 3 is a side view of such a conventional elevating device having a stop position fine adjustment.
In the device shown, with a base plate 7, which is fixed to a base frame, not shown, a photocoupler 5 is fixed.
On an elevating stand 2, a wafer basket 1 is placed, and the elevating stand 2 is vertically movable with respect to the basic frame of the device. The vertical movement is driven with an elevating motor, not shown.
The stand 2 is provided with an integral support plate 3 for an opaque plate 4 fixed to the support plate 3.
The elevating stand 2 is moved upwardly from its lowest position with respect to the basic frame of the device by the elevating motor, and when an upper end of the opaque plate 4 obstructs the optical path of the photocoupler 5, the motor is stopped to set an initial position.
In the opaque plate 4, slots 4a, 4b, are provided, so the relative position of the opaque plate 4 with respect to the elevating stand 2 may adjusted by loosening and re-tightening screws 3a, 3b, respectively. Thus, an initial position may be set.
In this example, adjustment of the initial stop position is possible. This adjustment must be made for each wafer basket used or at least each kind of wafer basket. The preciseness in the adjustment, on the order of 0.1 mm or so, must be maintained. The adjustment in this conventional device is however not simple.
An object of the present invention is therefore to provide a wafer basket having a semiconductor wafer sensing means, which can correctly detect the existence of a wafer or wafers in the basket, even if there are a variety of sizes or displacements of the center of the wafer or wafers.
Another object of the present invention is to provide a wafer basket having an elevating device with a stop position fine adjusting means, which can easily adjust the relative position of a photocoupler and an opaque plate, in order to set a stop position of the elevating device which can then vertically move the wafer basket in which wafers are received.